From 2d4215f75949448d5207ec67b11878741a708fbe Mon Sep 17 00:00:00 2001 From: Manman Ren Date: Sat, 7 Jul 2012 03:34:46 +0000 Subject: [PATCH] X86: Fix optimizeCompare to correctly check safe condition. It is safe if EFLAGS is killed or re-defined. When we are done with the basic block, check whether EFLAGS is live-out. Do not optimize away cmp if EFLAGS is live-out. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159888 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/X86/X86InstrInfo.cpp | 30 +++++++++++++++++++++++++----- test/CodeGen/X86/jump_sign.ll | 18 ++++++++++++++++++ 2 files changed, 43 insertions(+), 5 deletions(-) diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp index 7899985badc..f493438c29c 100644 --- a/lib/Target/X86/X86InstrInfo.cpp +++ b/lib/Target/X86/X86InstrInfo.cpp @@ -3107,22 +3107,28 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2, if (!Sub) return false; + bool IsSwapped = (SrcReg2 != 0 && Sub->getOperand(1).getReg() == SrcReg2 && + Sub->getOperand(2).getReg() == SrcReg); + // Scan forward from the instruction after CmpInstr for uses of EFLAGS. + // It is safe to remove CmpInstr if EFLAGS is redefined or killed. + // If we are done with the basic block, we need to check whether EFLAGS is + // live-out. + bool IsSafe = false; SmallVector, 4> OpsToUpdate; MachineBasicBlock::iterator E = CmpInstr->getParent()->end(); for (++I; I != E; ++I) { const MachineInstr &Instr = *I; - if (Instr.modifiesRegister(X86::EFLAGS, TRI)) + if (Instr.modifiesRegister(X86::EFLAGS, TRI)) { // It is safe to remove CmpInstr if EFLAGS is updated again. + IsSafe = true; break; - + } if (!Instr.readsRegister(X86::EFLAGS, TRI)) continue; // EFLAGS is used by this instruction. - if (SrcReg2 != 0 && Sub->getOperand(1).getReg() == SrcReg2 && - Sub->getOperand(2).getReg() == SrcReg) { - + if (IsSwapped) { // If we have SUB(r1, r2) and CMP(r2, r1), the condition code needs // to be changed from r2 > r1 to r1 < r2, from r2 < r1 to r1 > r2, etc. unsigned NewOpc = getSwappedConditionForSET(Instr.getOpcode()); @@ -3135,6 +3141,20 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2, // instructions will be modified. OpsToUpdate.push_back(std::make_pair(&*I, NewOpc)); } + if (Instr.killsRegister(X86::EFLAGS, TRI)) { + IsSafe = true; + break; + } + } + + // If EFLAGS is not killed nor re-defined, we should check whether it is + // live-out. If it is live-out, do not optimize. + if (IsSwapped && !IsSafe) { + MachineBasicBlock *MBB = CmpInstr->getParent(); + for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(), + SE = MBB->succ_end(); SI != SE; ++SI) + if ((*SI)->isLiveIn(X86::EFLAGS)) + return false; } // Make sure Sub instruction defines EFLAGS. diff --git a/test/CodeGen/X86/jump_sign.ll b/test/CodeGen/X86/jump_sign.ll index 567490b59ea..e84f49c8a1c 100644 --- a/test/CodeGen/X86/jump_sign.ll +++ b/test/CodeGen/X86/jump_sign.ll @@ -102,6 +102,24 @@ entry: %cond = select i1 %cmp, i32 %b, i32 %sub ret i32 %cond } +; If EFLAGS is live-out, we can't remove cmp if there exists +; a swapped sub. +define i32 @l2(i32 %a, i32 %b) nounwind { +entry: +; CHECK: l2: +; CHECK: cmp + %cmp = icmp eq i32 %b, %a + %sub = sub nsw i32 %a, %b + br i1 %cmp, label %if.then, label %if.else + +if.then: + %cmp2 = icmp sgt i32 %b, %a + %sel = select i1 %cmp2, i32 %sub, i32 %a + ret i32 %sel + +if.else: + ret i32 %sub +} ; rdar://11540023 define i32 @n(i32 %x, i32 %y) nounwind { entry: